ts-fold

Code-folding using tree-sitter

ts-fold builds on top of elisp-tree-sitter to provide code folding based on the tree-sitter syntax tree.

Table of Contents

• 💾 Installation
  • 🔍 Method 1. with straight.el and use-package:
  • 🔍 Method 2. Manual
• 🖥 Usage
  • 📇 Commands
  • 🔨 Supported languages
• 📝 Customization
  • ⚪ Folding on new nodes
    • ❔ Example
    • ↔ Offset
  • 🔍 Writing new fold functions
• 🔌 Plugins
  • ⚖️ Indicators Mode
    • 💾 Installation
    • 🖥 Usage
  • 📝 Summary
    • 🖥 Usage
    • 📝 Customization
  • 🌫️ Line-Comment folding
    • 🖥 Usage
• 🔰 Contribute
  • ❓ How to add a folding parser?
  • 🔍 Where can I look for tree-sitter node?
  • ❓ How to create a summary parser?

💾 Installation

🔍 Method 1. with straight.el and use-package:

(use-package ts-fold
  :straight (ts-fold :type git :host github :repo "emacs-tree-sitter/ts-fold"))

🔍 Method 2. Manual

git clone https://github.com/emacs-tree-sitter/ts-fold /path/to/lib

then in Emacs:

(add-to-list 'load-path "/path/to/lib")
(require 'ts-fold)

or

(use-package ts-fold
  :load-path "/path/to/lib")

🖥 Usage

📇 Commands

The following are the functions provided by ts-fold-mode

Commands for enabling ts-fold:

Commands for using ts-fold.

If evil mode is loaded, then these commands are also added to the evil folding list.

🔨 Supported languages

⚠️ Please sort these two lists alphabetically!

These languages are fairly complete:

• Bash
• C / C++ / C# / CSS
• Elixir
• Go
• HTML
• Java / JavaScript / JSX / JSON / Julia
• Lua
• Nix
• PHP / Python
• R / Ruby / Rust
• Scala / Swift
• TypeScript / TSX
• YAML

These languages are in development:

• Agda
• Elm
• Emacs Lisp
• OCaml
• XML (upstream)

📝 Customization

Although ts-fold aims to have good folding out of the box for all supported definitions, people will indubitably have their own preferences or desired functionality. The following section outlines how to add your own folding definitions and folding functions to make ts-fold work for you. If there are any improvements you find for existing or new languages, please do raise a PR so that others may benefit from better folding in the future!

⚪ Folding on new nodes

Ts-fold defines all its folding definitions in the variable ts-fold-range-alist which is an alist with the key of the alist being the mode and the value being another alist of fold definitions.

;; Example of ts-fold-range-alist's structure
'((c-mode     . c-folding-definitions) ;; <language>-folding-definitions is structured as shown below
  (css-mode   . css-folding-definitions)
  (go-mode    . go-folding-definitions)
  (scala-mode . scala-folding-definitions)
  ...)

;; Examle of a folding definition alist
(setq css-folding-definitions
    (block   . ts-fold-range-seq)
    (comment . ts-fold-range-c-like-comment))

So you can select whatever node that you want to fold on it.

To find what node you'll want to fold closed, refer to the tree-sitter documentation about viewing nodes. tree-sitter-debug and tree-sitter-query-builder are both very useful for this.

For the folding functions, ts-fold provides some default

• ts-fold-range-seq - Folds from the start of the node to the end of the node leaving a buffer of one character on each side. Usually used for code blocks that have bracketing delimiters.

  int main() { // <-- start of tree-sitter block node
      printf("Hello, World\n");
      return 0;
  } // <-- end of tree-sitter block node
  
  // |
  // | '(block . ts-fold-range-seq)
  // V
  
  int main() {...} // Folded node

• ts-fold-range-markers - Folds the node starting from a giving delimiter character. Useful if tree-sitter's node definition doesn't align with the start of the desired folding section.

  NOTE: This folding function requires a lambda (or an externally defined function wrapper) so that the delimiter can be specified. You usually don't need to worry about the node and offset variables, so just pass them through.

type Dog interface {
    Bark() (string, error)
    Beg() (bool, error)
}

/* | Note: The tree-sitter node starts at the word interface, not at the '{'.
 * | '(interface_type . (lambda (node offset)
 * |                      (ts-fold-range-markers node offset "{" "}")))
 * V
 */

type Dog interface {...}

• ts-fold-range-block-comment - Folds multi-line comments that are of the form /*...*/. Should show a summary if the commentary plugin is turned on.

  /*
   * The main function that gets run after program is compiled
   * Doesn't take any parameters
   */
  int main() {
      printf("Hello, World\n");
      return 0;
  }
  
  // |
  // | '(comment . ts-fold-range-block-comment)
  // V
  
  /* <S> The main function that gets run after program is compiled */
  int main() {
      printf("Hello, World\n");
      return 0;

• ts-fold-range-line-comment - For languages that have one line comment blocks with the comment delimiter starting each line. Condenses all the comment nodes into a single fold.

  Note: This folding function requires a lambda (or an externally defined function wrapper) so that the delimiter can be specified. You usually don't need to worry about the node and offset variables, so just pass them through.

  # show the long form of ls
  # and also display hidden files
  alias ll='ls -lah'
  
  # |
  # | (comment (lambda (node offset) (ts-fold-range-line-comment node offset "#"))))
  # V
  
  # show the long form of ls...
  alias ll='ls -lah'

• ts-fold-range-c-like-comment - A shortcut for the large number of languages that have the c style comment structures /*...*/ and // .... Smartly picks the correct folding style for the comment on the line.

  /*
   * The main function that gets run after program is compiled
   * Doesn't take any parameters
   */
  int main() {
      // print hello world
      // and a new line
      printf("Hello, World\n");
      return 0;
  }
  
  // |
  // | '(comment . ts-fold-range-c-like-comment)
  // V
  
  /* <S> The main function that gets run after program is compiled */
  int main() {
      // <S> print hello world
      printf("Hello, World\n");
      return 0;

Now that you know what kinds of folds are easily available in ts-fold, you can go ahead and add new fold definitions to ts-fold-range-alist and be good to go!

❔ Example

Let's look at a quick example of adding a new folding definition. Let's say you want to add folding to go-mode's field_declaration_list. The folding definition that is needed will be '(field_declaration_list . ts-fold-range-seq). To add this to the ts-fold-range-alist, you can do something like the following.

(push '(field_declaration_list . ts-fold-range-seq) (alist-get 'go-mode ts-fold-range-alist))

Now the new fold definition should be usable by ts-fold!

↔ Offset

With the functions listed above you'll be able to define most folding behavior that you'll want for most languages. However, sometimes you'll have a language where the delimiter is a word instead of a single character bracket and you want to offset your fold by a certain amount to accommodate it. That's where offsets come in. When adding a fold definition to a a language's fold alist, you can either provide the folding function directly as you've seen so far:

'(block . ts-fold-range-seq)

Or you can provide the folding function with an offset:

'(block . (ts-fold-range-seq 1 -3))

When a range is provided, it provides extra room on the ends of a fold. The way this works is most easily shown using an example. Lets say we want to write a fold for bash's for...do...done construct to look something like this:

for i in 1 2 3 4 5
do
   echo "Welcome $i times"
done

# |
# | '(do_group . <some folding function>)
# V

for i in 1 2 3 4 5
do...done

The do...done block is represented in tree-sitter as the node named do_group. However, if we just use '(do_group . ts-fold-range-seq), then we'll get results like the following:

for i in 1 2 3 4 5
d...e

which is hard to read. Instead, we can use the definition '(do_group . (ts-fold-range-seq 1 -3)) to offset the fold a bit to get our desired result!

🔍 Writing new fold functions

If the built in functions don't fit your needs, you can write your own fold parser! Folding functions take two parameters:

• node - the targeted tree-sitter node; in this example, block will be the targeting node.
• offset - (optional) a cons of two integers. This is handy when you have a similar rule with little of positioning adjustment.

Then the function needs to return a position range for the fold overlay in the form '(start-of-fold . end-of-fold). If nil is returned instead of a range, then no fold is created. This can be useful if you want to add extra conditional logic onto your fold.

As an example of a folding function, take a look at the definition of the basic ts-fold-range-seq.

(defun ts-fold-range-seq (node offset)
  "..."
  (let ((beg (1+ (tsc-node-start-position node)))  ; node beginning position
        (end (1- (tsc-node-end-position node))))   ; node end position
    (ts-fold--cons-add (cons beg end) offset)))    ; return fold range

🔌 Plugins

ts-fold comes with a couple of useful little additions that can be used or turned off as desired.

⚖ Indicators Mode

This plugin adds interactive visual markers in the gutter that show where folds can be made. They can be clicked on to fold or unfold given nodes.

💾 Installation

ts-fold-indicator-mode is loaded when ts-fold-mode is and the functionality should be auto-loaded in, however if that's not working then you may want to explicitly declare the package in in your config.

• use-package

  (use-package ts-fold-indicators
  :straight (ts-fold-indicators :type git :host github :repo "emacs-tree-sitter/ts-fold"))

• (add-to-list 'load-path "/path/to/lib")
  (require ts-fold)

  or

  (use-package ts-fold-indicators
     :load-path "/path/to/lib")

🖥 Usage

You can then enable this manually by doing either of the following:

M-x ts-fold-indicators-mode

M-x global-ts-fold-indicators-mode

Please note that turning on ts-fold-indicators-mode automatically turns on ts-fold-mode as well. Though, turning off ts-fold-indicators-mode does not turn off ts-fold-mode

• To enable this automatically whenever tree-sitter-mode is enabled, use the global indicator mode:

  (global-ts-fold-indicators-mode 1)

  Else, a hook can be added to tree-sitter directly.

  (add-hook 'tree-sitter-after-on-hook #'ts-fold-indicators-mode)

• To switch to left/right fringe: (Default is left-fringe)

  (setq ts-fold-indicators-fringe 'right-fringe)

• To lower/higher the fringe overlay's priority: (Default is 30)

  (setq ts-fold-indicators-priority 30)

• To apply different faces depending on some conditions: (Default is nil)

  For example, to coordinate line-reminder with this plugin.

  (setq ts-fold-indicators-face-function
        (lambda (pos &rest _)
          ;; Return the face of it's function.
          (line-reminder--get-face (line-number-at-pos pos t))))
  
  (advice-add 'line-reminder-transfer-to-saved-lines :after
              ;; Refresh indicators for package `ts-fold'.
              #'ts-fold-indicators-refresh)

📝 Summary

This plugin automatically extracts summary from the comment/document string, so you can have a nice way to peek at what's inside the fold range.

🖥 Usage

• If you don't want this to happen, do: (Default is t)

  (setq ts-fold-summary-show nil)

• Summary are truncated by length: (Default is 60)

  (setq ts-fold-summary-max-length 60)

• The exceeding string are replace by: (Default is "...")

  (setq ts-fold-summary-exceeded-string "...")

• To change summary format: (Default is " <S> %s ")

  (setq ts-fold-summary-format " <S> %s ")

📝 Customization

Just like with fold definitions, you can create your own summary definitions. Summary definitions are defined in ts-fold-summary-parsers-alist and has one summary function per major mode '(java-mode . fold-summary-function). The summary function takes in the doc string which is all the text from a doc node and then returns a string to be displayed in its stead. Unlike with the folding functions, there aren't a set of general summary functions to fall back on. However, there are lots of examples and helper functions present in ts-fold-summary.el. Let's look at one example here.

(defun ts-fold-summary-javadoc (doc-str)
  "Extract summary from DOC-STR in Javadoc."
  (ts-fold-summary--generic doc-str "*")) ;; strip the '*' and returns the first line

As can be seen ts-fold-summary--generic is a very helpful function since it removes the provided delimiter and returns the first line. often this will be enough.

🌫 Line-Comment folding

This plugin makes line comment into foldable range.

🖥 Usage

M-x ts-fold-line-comment-mode

🔰 Contribute

Enable tree-sitter-mode first, then tree-sitter-query-builder is useful to test out queries that determine what syntax nodes should be foldable and how to fold them. emacs-tree-sitter has an excellent documentation on how to write tree-sitter queries.

❓ How to add a folding parser?

When adding a new folding parser, add the folding definition function to ts-fold.el itself near where the other range functions live and then add the parser to ts-fold-parsers.el file. Finally, if you are adding support for a new language, remember to add it to the ts-fold-range-alist variable.

When creating a new parser, name it ts-fold-parsers-<language>.

When creating a new folding function, name it ts-fold-range-<language>-<feature> or something similar.

🔍 Where can I look for tree-sitter node?

Here are some techniques for finding your desired nodes in tree-sitter.

To look for the correct node you have three options:

• look at the tree-sitter-[lang]/grammar.js implementation. In the above example, block node is defined in the tree-sitter-c-sharp's grammar.js file
• open a file of your language choice in emacs and M-x tree-sitter-debug-mode. This will display the whole s-expr representing your file
• (message "%S" (tsc-node-to-sexp)) in your function to display what your function is seeing

⚠️ Warning

Make sure you look into the correct repository. Repositories are managed under tree-sitter-langs's using git submodule. Some tree-sitter module aren't using the latest version!

❓ How to create a summary parser?

ts-fold-summary.el module is used to extract and display a short description from the comment/docstring.

To create a summary parser, you just have to create a function that could extract comment syntax correctly then register this function to ts-fold-summary-parsers-alist defined in ts-fold-summary.el. The display and shortening will be handled by the module itself.

Functions should be named with the prefix ts-fold-summary- followed by style name. For example, to create a summary parser for Javadoc style, then it should be named ts-fold-summary-javadoc.